This invention relates to ventilation systems, and more particularly, to induction ventilation systems.
Conventional induction ventilation systems inject a constant volume flow of primary air into a room or zone induction unit duing all periods of operation. In such systems, the primary air flows through the induction nozzles in the induction unit, thereby causing secondary air from the zone to be induced into the induction unit. The combined air flow passes at a relatively fixed flow rate over a heat exchanger and then from the induction unit into the zone. Generally, the heat exchanger includes a central core portion, such as a water coil, and a plurality of convection elements connected thereto in order to promote relatively efficient heat exchange between the primary and secondary air and water passing through the coil. The flow of water through the heat exchanger is generally controlled by a pneumatically operated valve which is modulated in response to a pneumatic thermostatic device to achieve a desired temperature control for the zone.
During the cooling season, a constant flow rate of primary air is supplied to the zone induction unit, and a flow of cold water is supplied to the coil at a rate which is modulated to provide a desired cooling capacity. Typically, prior art systems utilize a water valve at the water coil which is normally open, with a thermostatic device causing the valve to close partially depending on the temperature within the zone. In this cooling mode, an increase in temperature in the zone causes a decrease in control air pressure to the thermostat with a resultant increase in chilled water flow through the heat exchanger.
During the heating season, prior art systems supply a constant volume of primary air to the zone induction unit while the water supply to the coil is maintained at a relatively high temperature through the passage of hot water. The action of the thermostatic device is changed with respect to the cooling system operation in order to be direct acting, whereby a decrease in temperature causes a decrease in thermostat air pressure, which in turn opens the valve to the water coil with a resultant increase in hot water flow to the heat exchanger.
With these configurations, prior art systems are subject to substantial disadvantages. First the same volume of primary air must be continually conditioned from its ambient condition. Since typical systems utilize outside air for the primary air, there is often a relatively large temperature differential required to transform that air to the desired room temperature. As a result, the energy consumption in conditioning this relatively large volume of air is relatively high. Furthermore, relatively large amounts of energy are required to continually drive this air past the heat exchanger.
Accordingly, it is an object of the present invention to provide an induction ventilation system with relatively low energy demands compared with prior art systems.
Another object of the present invention is to provide an induction ventilation system utilizing a selectively controlled flow rate of primary air.